This invention relates to quick-fastening nuts and has particular, though not exclusive, application to reaction nuts associated with hydraulic bolt tensioning tools.
A bolt tensioning tool is essentially a hydraulic jack positioned over a nut and bolt assembly with the bolt extending centrally through the tool. In order to apply a load t the bolt, the tensioning tool must react against a nut screwed onto the bolt above the tool.
The length of the portion of the bolt protruding above the tool can be significant and, particularly in restricted and/or hazardous environments, such as underwater or in the nuclear industry, screwing of the reaction nut onto or from the bolt can be a time consuming and exhausting procedure, especially on larger diameter bolts with fine threads.
There are numerous other situations where two components are joined together by one or more nut and bolt assemblies and in which the free end extent of the bolt protrudes some distance beyond the associated component whereby it is necessary to screw the nut over a considerable distance before the joint is effected. Again, this can prove a time consuming exercise.
In order to overcome this problem, it has been proposed, for example in U.S. Pat. No. 4083288, to provide a split nut comprising two half nuts which can be located on a bolt at any axial position therealong, the split nut being provided with a conical surface thereon for cooperation with a complementary recess in a washer or other workpiece. On tightening, the components of the split nut are held together and in threaded engagement with the bolt by co-operation between the conical surface thereon and the recess in the workpiece.
This concept has been applied to hydraulic bolt tensioners, for example as disclosed in U.S. Pat. No. 4438901 and UK patent specification no. 2143608 in which the puller of the tensioner incorporates a collet consisting of a plurality of segments.
A hydraulic bolt tensioner incoporating a simplified puller in the form of a split nut provided with a cam surface thereon for engagement by a complementary recess in the piston of the hydraulic piston-cylinder assembly is disclosed in UK patent specification no. 2193549.
These known split nuts all suffer from the major disadvantage that they initially require the application thereto of an external radially-inwardly directed force to maintain threaded engagement with the associated bolt -- i.e. in the absence of such a force, the components of the split nut, being separate from one another, become disengaged from the bolt.
Thus it will be appreciated that it is very difficult, if not impossible, to use such split nuts in upside down or even horizontal situations, while, in the application of these known split nuts to hydraulic bolt tensioners in such inverted or horizontal situations, it is necessary to hold onto both the tensioner and the nut until positive cooperation between the piston and the nut has been effected.
A split nut comprises at least two segments and it is essential that the segments actually associated with one another are combined to comprise a given split nut -- using other than the correct segments in combination with one another can lead to problems in matching the threads of the segments.
With the known arrangements, particularly in mass production of the split nuts in question and because of the entirely separate nature of the segments, it is easy to mismatch the segments and to end up with a nut comprising incompatible segments.